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Issue 15, 2020

Uncovering friction dynamics using hydrogel particles as soft ball bearings

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Rolling ball bearings are widely known and applied to decrease friction between two surfaces. More recently, hydrogel–hydrogel tribopairs have also revealed good but rather complex lubrication properties. Here, we use hydrogels as ball bearings to elucidate that soft spherical particles have nontrivial rate-dependent lubrication behavior. Unlike Newtonian lubrication or dry solid friction, hydrogel particles in suspension transition through four frictional regimes as a function of sliding velocity. We relate the different regimes to the deformation of the particles at different gap sizes, which changes the effective contact area between the sliding surfaces. By systematically varying the particle characteristics and the surface properties of the sliding surfaces, we assign potential mechanisms for each of the different lubricating regimes as a function of velocity: (I) relatively high friction due to particle flattening and direct contact between interacting bodies (II) decrease of friction owing to the presence of rolling particles (III) large inflow of particles in a confined space leading to compressed particles and (IV) the formation of a thick lubricating layer. Using these suspensions with soft, deformable particles as a ball bearing system, we provide new insights into soft material friction with applications in emulsions, powders, pastes or other granular materials.

Graphical abstract: Uncovering friction dynamics using hydrogel particles as soft ball bearings

Article information

13 Jan 2020
16 Mar 2020
First published
19 Mar 2020

This article is Open Access

Soft Matter, 2020,16, 3821-3831
Article type

Uncovering friction dynamics using hydrogel particles as soft ball bearings

R. E. D. Rudge, J. P. M. van de Sande, J. A. Dijksman and E. Scholten, Soft Matter, 2020, 16, 3821 DOI: 10.1039/D0SM00080A

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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